CLASS 11 BIOLOGY CHAPTER 6 ANATOMY OF FLOWERING PLANTS
ANATOMY OF ROOT:
INTERNAL STRUCTURE OF DICOT ROOT (T.S):
EPIBLEMA:
1. Outermost layer. 2. Single layer. 3. Epiblema give rise to unicellular root hairs.
CORTEX:
1. This layer is next to epiblema. 2. It is made of parenchyma cells. 3. It has several layers. 4. It contains starch grains.
ENDODERMIS:
1. Single layer inner to cortex. 2. It has barrel shaped cells which have casparian thickenings. 3. Endodermis cells against protoxylem are thin walled called passage cells.
PERICYCLE: 1. Single layer inner to endodermis. 2. Thin walled cells.
VASCULAR TISSUE:
1. Xylem alternates with phloem. 2. Xylem is exarch (protoxylem towards the periphery and metaxylem towards the centre). 3. 2 to 6 strands of xylem. 4. Parenchyma cells present between xylem and phloem.
PITH:
1. It occupies the central part of root. 2. It is made up of thin walled parenchyma cells. 3. It is poorly developed.
INTERNAL STRUCTURE OF MONOCOT ROOT:
EPIBLEMA: 1. Outermost layer. 2. Single layer. 3. This give rise to unicellular root hairs.
CORTEX:
1. This layer is next to epiblema. 2. It is made of parenchyma cells. 3. It has several layers. 4. It contains starch grains.
ENDODERMIS:
1. Single layer inner to cortex. 2. It has barrel shaped cells which have casparian thickenings. 3. Endodermis cells against protoxylem are thin walled called passage cells.
PERICYCLE:
1. Single layer inner to endodermis. 2. Thin walled cells.
VASCULAR TISSUE:
1. Xylem alternates with phloem. 2. Xylem is exarch. 3. 6 to 20 strands of xylem. 4. Parenchyma cells present between xylem and phloem.
PITH:
1. It occupies the central part of root. 2. It is made up of thin walled parenchyma cells. 3. Pith is well developed.
T.S OF DICOT STEM:
EPIDERMIS:
1. Outermost layer made of tangentially elongated cells. 2. Multicellular hairs and stomata present on epidermis. 3. Epidermis is lined by cuticle.
CORTEX: It has several layers which are classified as follow:
a. HYPODERMIS: 1. Outermost region of cortex. 2. 3 to 5 layers. 3. Made up of collenchyma cells. 4. Compact cells which contain chloroplasts. b. GENERAL CORTEX: 1. It is the middle layer of cortex. 2. It has several layers. 3. Made up of parenchyma cells with intercellular spaces. c. ENDODERMIS: 1. Innermost layer of cortex. 2. Barrel-shaped cells with starch deposit. 3. This zone is called starch sheath.
PERICYCLE:
1. It is a single layer next to endodermis. 2. Made up of sclerenchyma cells.
VASCULAR BUNDLES:
1. Vascular bundles are arranged in a ring. 2. Xylem is endarch(protoxylem towards the centre and metaxylem towards the periphery. 3. Vascular bundles are conjoint, collateral and open. 4. Xylem is composed of vessels, tracheids, xylem fibres and xylem parenchyma. 5. Phloem is made up of sieve tubes, companion cells and phloem parenchyma. 6. Cambium is present between xylem and phloem. 7. Cambium is made up of meristematic cells.
PITH:
1. It occupies the central part. 2. Thin walled parenchyma cells. 3. Intercellular spaces present.
T.S OF MONOCOT STEM
EPIDERMIS:
1. Outermost layer, single layer. 2. Composed of parenchyma cells. 3. Stomata is present.
HYPODERMIS: 1. 2 to 3 layers. 2. Made up of sclerenchyma cells
GENERAL TISSUE: 1. Vascular bundles are scattered. 2. Vascular bundles are conjoint, collateral a closed(cambium absent). 3. Xylem appears as Y shaped. 4. Ground tissue is made up of parenchyma cells.
VASCULAR BUNDLES:
1. Numerous vascular bundles are scattered in the ground tissue. 2. Vascular bundles are conjoint, collateral and closed. 3. Each vascular bundle is surrounded by a sclerenchymatous sheath. 4. Xylem is composed of vessels, tracheids and xylem parenchyma. 5. Phloem is made up of sieve tubes and companion cells.
ANATOMY OF LEAF:
V.S. OF DICOT LEAF:
The leaf has three tissue systems, the DERMAL SYSTEM (upper and lower epidermis), the GROUND TISSUE SYSTEM, the main photosynthetic tissue which consists of mesophyll and the VASCULAR SYSTEM, comprising veins of various degrees. EPIDERMIS:
1. Single layer of epidermis is present on the upper and lower surface of the leaf. 2. Stomata is present on this region. 3. Epidermis is surrounded by cuticle.
MESOPHYLL:
1. These cell layers are present between upper and lower epidermis. 2. Made up of parenchyma cells. 3. Numerous chloroplasts present. 4. In dorsiventral leaf, Mesophyll layer is differentiated into upper palisade and lower spongy cells. 5. Palisade cells are elongated and compact whereas spongy cells are irregular and have intercellular spaces between them.
VASCULAR SYSTEM:
1. Collateral vascular bundle present. 2. It is surrounded by thin walled parenchyma cells.
V.S. OF MONOCOT LEAF:
1. Stomata present on both upper and lower surface. 2. Mesophyll occupies the cells between upper and lower epidermis. 3. Mesophyll cells are irregular shaped with large intercellular spaces. 4. The cavity above the stoma is called sub-stomatal chamber. 5. Vascular bundle is surrounded by double layer of bundle sheath.
QUESTIONS-ANSWERS:
Q1. Draw illustrations to bring out the anatomical difference between:
a. Monocot and dicot root. b. Monocot and dicot stem.
A1.
Q2. With the help of suitable examples, describe the various types of vascular bundles in plants.
A2. On the basis of relative position of xylem and phloem, following types of vascular bundles are there:
1. Radial: vascular bundles are arranged alternately on different radii. 2. Collateral: xylem and phloem are on the same radii. Phloem is on the outer side. In dicot stems, open type and monocot stem has closed type. 3. Bicollateral: A vascular bundle with both external and internal phloem . 4. Concentric: one type of vascular bundle is surrounded by the other.
Q3. Describe the steps of secondary growth in dicot stem.
A3.
(i) Origin and formation of vascular cambium: A strip of cambium that originates from the procambium is present between xylem and phloem of vascular bundle. This cambial strip is called intrafascicular cambium. At the onset of secondary growth, additional strips of cambium are formed from the interfascicular parenchyma between the vascular bundles. These later formed strips of cambium , called interfascicular cambium. This cambial cylinder produces secondary phloem towards the outer side and secondary xylem towards the inner side . (ii) Activity of vascular cambium: The initiation of secondary vascular tissue occurs after the maturation of primary xylem and phloem. At this stage, cambium is represented by a single layer of cells. The fusiform initials of the cambium divide vertically, each forming two daughter cells. One of thye daughter cells remains meristematic while the other differentiates into xylem or phloem element. The cells which are produced outward from phloem elements, and those inward xylem elements. The ray initials of cambium cut plates of parenchymatous cells both outward and inward. These are secondary medullary rays which extend horizontally from the pith to the secondary xylem and phloem. (iii) Activity of phellogen(cork cambium) in extrastelar region: As more and more secondary xylem is formed outwards, the tissues outside it become increasingly compressed and stretched sideways by the increasing circumference. This effects the epidermis, cortex and primary phloem. The epidermis ruptures and is replaced by a protective tissue called Periderm. Periderm is formed by phellogen or cork cambium. The periderm includes the phellogen (cork cambium) and its two derivatives, the phellem (cork) and phelloderm (secondary cortex).
Q4. Explain the formation of Periderm.
A4. During the secondary growth in dicot stem, epidermis ruptures and form a protective tissue called Periderm. . Periderm is formed by phellogen or cork cambium. The periderm includes the phellogen (cork cambium) and its two derivatives, the phellem (cork) and phelloderm (secondary cortex).
(i) Phellogen(cork cambium): It is a secondary lateral meristem. It usually originates superficially in the sub-epidermal layer or even in the epidermis itelf. Hiostoligically, phellogen is relatively simple and is composed of only one type of cells. The cells of phellogen appear almost rectangular in a cross section. They are highly vacuolated. They divide periclinally as phellem(cork) and those towards the inside as pheloderm(secondary cortex). (ii) Phellem (cork) : The cells of the phellogen are dead at maturity and thay are characterized by suberin deposits on their walls. They are usually prismatic in shape and are arranged compactly in radial rows. Sometimes, non-suberised cells, known phelloids, also occur in the cork. (iii) Phelloderm(secondary cortex): The cells of phelloderm are living with non-suberised cellulose walls which have simple pits.
Q5. Differentiate between anticlinal and periclinal cell division.
A5. The plane of division of cells, at right angles to outer surface of plant part is known as anticlinal division. On the other hand , the plane of division of cells, running parallel to the surface of plant part is known as periclinal division.
Q6. Differentiate between heartwood and sapwood. A6. Outer light coloured region of the wood is distinct from the inner dark coloured region. The former is known as sapwood and the latter heartwood.
The sapwood consists of living cells, whereas the heartwood is composed of dead cells which become impregnated with resins, gummy or tannin like substances.
Q7.Name the plant from which an important pigment of commercial importance, obtained from the heartwood.
A7. Acacia catechu, tannin(Catechu) obtained from heartwood used with paan; and for dyeing cloth.
ACTIVITIES: learn the topics with the help of diagrams.